1. Field of the Invention
The present invention relates to a film formation method and apparatus for a semiconductor process for forming an oxide film on a target substrate, such as a semiconductor wafer. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target substrate, such as a semiconductor wafer, is subjected to various processes, such as film formation, etching, oxidation, diffusion, reformation, annealing, and natural oxide film removal. For example, where a silicon oxide film is formed on semiconductor wafers, tetraethoxysilane (TEOS: Si(OC2H5)4) may be used to perform a CVD (Chemical Vapor Deposition) process as a film formation process in a vertical heat processing apparatus (of the so-called batch type).
In recent years, owing to the demands of increased miniaturization and integration of semiconductor integrated circuits, it is required to alleviate the thermal history of semiconductor devices in manufacturing steps, thereby improving the characteristics of the devices. For vertical processing apparatuses, it is also required to improve semiconductor processing methods in accordance with the demands described above. For example, there is a CVD process which performs film formation while intermittently supplying a source gas and so forth to repeatedly form layers each having an atomic or molecular level thickness, one by one, or several by several. In general, this film formation method is called ALD (Atomic Layer Deposition) or MLD (Molecular Layer Deposition), which allows a predetermined process to be performed without exposing wafers to a very high temperature. Further, the ALD or MLD film formation provides good step coverage, and thus is suitable for filling recess portions of semiconductor devices, such as inter-gate gaps, which have become narrower with increased miniaturization of the devices. For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-281853 (Patent Document 1) discloses a method of forming a silicon nitride film by ALD at a low temperature of 300 to 600° C.
On the other hand, where oxide films, such as a silicon oxide film, are thinner along with increased miniaturization of the devices, they may cause various problems depending on the quality. For example, where a gate oxide film is thinner, a leakage current may be increased if the film quality is not good.